STUDY ON THE CONSTRAINT EFFECT USING THE DAMAGE MECHANICS APPROACH.

(1)通过改变约束条件，进行了断裂韧性试验。断裂韧度值是一个宏观参数，受约束条件的影响。通过扫描电镜（SEM）对断口形貌的观察发现，约束条件对微观参数如韧窝直径、韧窝数量和功率值也有很大影响。(2)对不同缺口半径的缺口试样进行了韧窝断裂试验。断口观察表明，应力三轴度对韧窝断裂过程也有很大影响。应力三轴度的变化意味着约束条件的变化。对凹坑直径和深宽比进行了精确测量，获得了3000多个数据。这是该研究领域数据库的基础。(3)采用有限元法对韧窝断裂进行了数值模拟，考虑了损伤力学效应。使用该代码模拟（1）和（2）中描述的两种测试。结果表明，约束效果评价良好。该程序可以考虑基体中夹杂物的非均匀分布对计算结果的影响。夹杂物分布的不均匀性对韧窝断口形貌有很大的影响。(4)从而进一步明确了约束条件与细观韧性断裂过程的关系，为从细观断裂力学角度研究约束条件奠定了基础。

(1) By changing the constraint condition, fracture toughness tests are conducted. The fracture toughness value, which is a macroscopic parameter, is affected by the constraint condition. By the observation of fracture surface using scanning electron microscope(SEM), it was shown that the microscopic parameter such as dimple diameter, dimple number and power value are also affected by the constraint condition largely.(2) The dimple fracture tests of notched specimen with different notch radius are conducted. The fracture surface observation showed that the stress triaxiality also affects the dimple fracture process strongly. The change of the stress triaxiality means the change of the constraint condition. Precise measurement of the dimple diameter and dimple aspect ratio is made, and more than 3000 data are obtained. It is base of the data-base on this research area.(3) The dimple fracture simulation is conducted using FEM considering the damage mechanics effect. Two kinds of tests described in (1) and (2) are simulated using this code. It is shown that the constraint effect was evaluated well. The effect of the non-uniform distributions of inclusions in the base matrix can be considered using this code. It became obvious that the non-uniform distribution of inclusions affects the dimple fracture pattern largely.(4) As a result, the relation between the constraint condition and the microscopic ductile fracture process is becoming clear, which is the basis of the study on the constraint condition from the microscopic fracture mechanics.